The present invention relates to MacPherson strut assemblies, and more particularly, to an improved apparatus and method of repairing certain MacPherson strut assemblies.
MacPherson strut assemblies are commonly used as a part of the suspension systems for modern automobiles and related vehicles. Typically, such assemblies are used for the vehicle front or steering suspension and to support the vehicle body, also known as the "sprung" mass, upon the vehicle chassis, also known as the "unsprung" mass. The advantages of using MacPherson strut assemblies in such applications are numerous and well known to persons having skill in this art.
The design of MacPherson strut assemblies varies from manufacturer to manufacturer. In certain MacPherson strut assemblies used in various models of automobiles sold during the late 1970's and early 1980's, the MacPherson strut assemblies included a piston rod whose upper end was attached, through a upper housing support assembly, to the vehicle body. In these strut assemblies, the support housing assembly included a first member which was attached to the vehicle body and a second member which was connected with the piston rod so that the piston rod acts against this second member. A rubber member was disposed between and was secured to the first and second members of the support housing assembly by a vulcanization process. An annular, inverted bell shaped retainer member was used to secure the support housing assembly to the upper end of the piston rod. More particularly, the piston rod extends through the central opening in the retainer member. The otherwise closed end of the retainer member extends through the central opening in the first member so that the side of the retainer member snugly abuts the first member. A nut, threaded onto the upper end of the piston rod holds the retainer member tightly against the first member.
The intended purpose of the inclusion of the rubber member in the support housing assembly was to minimize the transmission of noise and vibrations between first and second members and thus between the strut assembly and the vehicle body. While initially the aforementioned strut assemblies apparently performed satisfactorily, an increasing number of owners and operators of models with these strut assemblies began complaining about the noise and vibration they were experiencing during the normal operation of their vehicles. This noise and vibration problem made driving, and particularly steering, unpleasant. The problem seemed to begin to occur after about one year of normal usage of the vehicles, or more specifically, after the strut assemblies had experienced from 200,000 to 400,000 cycles of usage, as compared to a normal life expectancy of well over one million cycles.
It was fairly easy for mechanics to identify the strut assembly as the cause of this objectionable noise and vibration problem. The difficulty was how to repair or correct the problem. This increasingly became a significant, widespread problem as the models having these strut assemblies aged.
Typically, an initial response by a mechanic to such a complaint was to tighten the nut that was threaded on the upper end of the piston rod and that served to hold the retainer member against the first member of the support housing assembly. Such tightening does not remedy the problem for long if at all. Ordinarily the next repair attempt involved the replacement of the "cartridge", that is, the strut cylinder, pressure cylinder and piston rod. The cost of this repair work was generally around $90.00 to $150.00 per model. Such replacement also does not solve the problem.
The next attempted repair involved the replacement of the upper support housing assembly. The cost of this was generally in the range of $90.00 to $100.00 per model and did temporarily remedy the problem. Nevertheless, the problem often reoccurred after the strut assemblies had been used for another 200,000 to 400,000 cycles, again well short of their anticipated normal life expectancies.
Generally one of the results of the unsuccessful attempted repairs and the temporary repair is that the car owner becomes quite frustrated and angry. The goodwill of the automobile manufacturer, as well as that of the manufacturer of the replacement parts, suffers even where the replacement of the support housing assembly "fixes" the problem.